1. Field of the Invention
The present invention relates to a photoelectric sensor provided with a display part.
2. Description of Related Art
There are the following types of photoelectric sensors: a first-type photoelectric sensor that detects presence or absence of an object to be detected (hereinafter, referred to as “workpiece”) based on a light reception amount of received light; and a second-type photoelectric sensor that detects the presence or absence of a workpiece mainly based on a distance to the workpiece. The second-type photoelectric sensor is called a “distance setting photoelectric sensor”. JP 2005-210720 A (JP 4023621 B2) and U.S. Pat. No. 6,555,806 disclose the first-type photoelectric sensor. JP 2007-33097 A discloses the second-type photoelectric sensor.
Based on their shapes, the photoelectric sensors can be roughly classified into a box-type photoelectric sensor (U.S. Pat. No. 6,555,806) and a slim-type photoelectric sensor (JP 2005-210720 A and JP 2007-33097 A). FIG. 37 shows a photoelectric sensor disclosed in U.S. Pat. No. 6,555,806 as a typical example of the box-type photoelectric sensor. FIG. 38 shows a photoelectric sensor disclosed in JP 2007-33097 A as a typical example of the slim-type photoelectric sensor.
Referring to FIG. 37 that discloses the box-type photoelectric sensor, reference numeral 1 denotes a head unit, reference numeral 2 denotes a main unit, and this main unit 2 corresponds to the box-type photoelectric sensor. The main unit 2 has an amplifier built therein. The head unit 1 is connected to the main unit 2 via cables 3a, 3b. 
The sensor head unit 1 emits laser light, which falls on a workpiece W and is reflected thereon, and the sensor head unit 1 receives the reflected light. The main unit 2 compares a light reception amount (current value) of the light received by the sensor head unit 1 with a previously set threshold, to detect the presence or absence of the workpiece.
The main unit 2 has a top surface 2a, namely, an operation surface, in a rectangular shape in a plan view, and a central region of this top surface 2a is provided with a first display section 4 and a second display section 5 both extending in a lateral direction. The first and second display sections 4, 5 are each configured by a seven-segment LED. As can be understood from FIG. 37, comparatively large-sized numerals are displayed on the first display section 4 located in a relatively upper portion, whereas small-sized numerals are displayed on the second display section 5 located in a lower portion.
On the top surface 2a of the main unit 2, a bar display section 6 is disposed using a plurality of indicating lamps (LED) laterally arranged in an upper left portion, and a laser-emitting indicator 7 is disposed below this bar display section 6.
On the top surface 2a of the main unit 2, hold mode indicators 8a, 8b are also disposed on the left of the second display section 5. On the top surface 2a of the main unit 2, a mode switch 9 and a setting switch 10 are further disposed on the right of the first and second display sections 4, 5, and below the mode switch 9 and the setting switch 10, there is disposed an adjustment switch 11 including an up-switch 11u and a down-switch 11d which are laterally arranged. An output of the main unit 2 is performed through a cable denoted by reference numeral 12.
Referring to FIG. 38 that discloses the slim-type photoelectric sensor, reference numeral 20 denotes a head unit and reference numeral 21 denotes a main unit. This main unit 21 corresponds to the distance setting photoelectric sensor. The head unit 20 has a light projection element configured by a laser diode, and a light reception element whose light reception surface is configured by a two-divided PD (photodiode). One divided light reception surface constitutes an N-side (Near-side) light reception surface, and the other divided light reception surface constitutes an F-side (Far-side) light reception surface. A difference between a light reception amount of the N-side light reception surface and a light reception amount of the F-side light reception surface is supplied from the head unit 20 to the main unit 21 through a first cable 22. Further, a drive control signal of the light emitting element is supplied from the main unit 21 to the head unit 20 through a second cable 23 that connects between the head unit 20 and the main unit 21.
The main unit 21 calculates a detected distance of the workpiece W based on the difference between the light reception amount of the N-side light reception surface and the light reception amount of the F-side light reception surface (the difference in light reception amount) received from the head unit 20.
A narrow display section 24 is disposed in a central portion in a longitudinal direction of a narrow top surface 21a, namely, an operation surface, of the main unit 21. The display section 24 is configured by an eight-digit seven-segment LED. An indicator 25 for displaying a result of comparison between a detected distance and a standard distance is disposed in one end section in the longitudinal direction of the narrow top surface 21a. Further, one button switch 26 is disposed adjacent to one end in a longitudinal direction of the display section 24, and a swing switch 27 is disposed adjacent to the other end of the display section 24. Moreover, another button switch 28 is disposed in the other end section of the main unit 21. By use of these switches 26 and 27, a display mode of the display section 24 can be switched, a variety of setting can be made, and a set value can be adjusted. In addition, in FIG. 38, reference numeral 29 denotes an output cable, and reference numeral 30 denotes a lid.
JP 2005-210720 A relates to a slim-type photoelectric sensor, and gives a detailed description of items which are displayed on first and second display sections and shifts of the displays when the eight-digit seven-segment LED is divided into two to form two display sections, i.e., the first and second display sections. For example, there is disclosed an example where a “current value (light reception amount)” is numerically displayed on the first display section and a “threshold” is numerically displayed on the second display section.
As can be easily understood from the detailed descriptions of JP 2005-210720 A, U.S. Pat. No. 6,555,806, and JP 2007-33097 A, as well as FIGS. 37 and 38, the indicator, the display section (seven-segment LED), and the variety of switches are arranged on the top surface 2a (FIG. 37) or 21a (FIG. 38) having a limited area in either the box-type photoelectric sensor (FIG. 37) or the slim-type photoelectric sensor (FIG. 38).
Meanwhile, the photoelectric sensor has been made more multi-functional and further reduced in size. With the multi-functionalization and size reduction in progress, the number of switches cannot be increased. Naturally, it is not permissible to make improvements that lead to deterioration in user's operability. From the viewpoint of the user's operability, as seen in JP 2005-210720 A, U.S. Pat. No. 6,555,806, and JP 2007-33097 A, there have been made a variety of efforts as follows: allocating several functions respectively to a limited number of switches; shifting a numerical value displayed on the display section using the seven-segment LED; displaying characters that can be displayed with the seven-segment LED so that a meaning of each numerical value can be visually understood; and the like. Typical examples of the above include: dividing the eight-digit seven-segment LED into two sections to simultaneously display different kinds of items (information), as disclosed in JP 2005-210720 A; and operating a limited number of switches to shift an item (information) to be displayed on the display section or adjust the displayed set value.